One method that currently works is to tag islands as part of the same way as the riverbanks, but make them go anti-clockwise.<br><br>So you have one way that goes up the left bank of the river for, say, 1km then goes down the right bank for for the same distance. If the two riverbanks are imagined to be part of a closed way then the segments should point in a clockwise direction. Then all of the islands within that 1km section are also made part of that same way, but tagged in an anti-clockwise direction.
<br><br>This seems to work pretty well, even when cut at arbitrary points by a bbox, and is understood by SVG so renders with Osmarender. The same principle also workd for islands in lakes and any other situation where something has a "hole" in it.
<br><br>There are some examples along the River Thames:<br><br>Simple example: <a href="http://www.informationfreeway.org/?lat=6698535.88756&lon=-57979.86205&zoom=16&layers=B000">http://www.informationfreeway.org/?lat=6698535.88756&lon=-57979.86205&zoom=16&layers=B000
</a><br>Complex example: <a href="http://www.informationfreeway.org/?lat=6688981.2611&lon=-51110.08562&zoom=16&layers=B000">http://www.informationfreeway.org/?lat=6688981.2611&lon=-51110.08562&zoom=16&layers=B000
</a><br><br>80n<br><br><div><span class="gmail_quote">On 4/14/07, <b class="gmail_sendername">David Groom</b> <<a href="mailto:reviews@pacific-rim.net">reviews@pacific-rim.net</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div bgcolor="#ffffff">
<div><font face="Arial" size="2">I don't know :)</font></div>
<div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">I've been meaning to update the large
rivers page [1] to get debate going on the whole large rivers /
lakes idea, which would include a discussion on how to render
islands.</font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">Straying away from your initial question, and
looking at large rivers, Osmarender currently renders large rivers, but the
Mapnik layer does not.</font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">As I understand it Mapnik needs a proper polygon to
generate the fill and so does not generate a filled wide river from the proposed
rendering on the large rivers [1] page. </font><font face="Arial" size="2">Own its own this is fairly easy to implement.</font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">Moving now to your question about islands
:</font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">It is, as far as I can see, fairly difficult to
intuitively split a river with islands in it into polygons (particularly where
there are many islands close to each other) , where each polygon would be a
continuous way and there is not a complicated system of segments going between
the riverbank and each island. </font> </div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">I'd like to see a modification of my proposal on
the large rivers page [1] where riverbanks would be drawn as a polygon with
a tag something like waterway = riverbank, and islands in these rivers
woul</font><font face="Arial" size="2">d be drawn as waterway = riverbank; island =
yes. Given this suggested rendering, island in lakes could be tagged
exactly the same as islands in rivers and they would still render
correctly.</font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">David</font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">[1] <a href="http://wiki.openstreetmap.org/index.php/Proposed_features/Large_rivers" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://wiki.openstreetmap.org/index.php/Proposed_features/Large_rivers
</a></font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2"></font> </div>
<blockquote style="border-left: 2px solid rgb(0, 0, 0); padding-right: 0px; padding-left: 5px; margin-left: 5px; margin-right: 0px;"><div><span class="e" id="q_111edaba83ee914b_1">
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">----- Original Message ----- </div>
<div style="background: rgb(228, 228, 228) none repeat scroll 0% 50%; -moz-background-clip: -moz-initial; -moz-background-origin: -moz-initial; -moz-background-inline-policy: -moz-initial; font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">
<b>From:</b>
<a title="lewispusey@earthlink.net" href="mailto:lewispusey@earthlink.net" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">lewispusey</a> </div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>To:</b> <a title="talk@openstreetmap.org" href="mailto:talk@openstreetmap.org" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
talk@openstreetmap.org</a> </div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>Sent:</b> Friday, April 13, 2007 5:08
PM</div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>Subject:</b> [OSM-talk] Islands</div>
<div><br></div>
<div><font face="Arial" size="2">What is the current best way to draw and tag
islands in rivers and lakes?</font></div>
<div><font face="Arial" size="2">Lewis</font></div></span></div>
<p>
</p><hr>
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